lambda expression with nullable value - always false since the value of type Guid is never equal to-CodePudding

public class Car
{
    public int Id {get; set;}
    public Guid? OwnersId { get; set; }
    ...
}

I'm trying to fetch all car data upon criteria

List<Car> cars = await carsContext.Query(x=>x.Id== model.CarId && x.OwnersId.Value == null);

The result of the expression is always false since the value of type Guid is never equal to 'null' of type 'Guid?'

CodePudding user response：

Value property of Nullable<T> struct returns value of the underlying type (Guid in your case) which can not be null. Compare the OwnersId itself to null:

List<Car> cars = await carsContext
    .Query(x => x.Id == model.CarId && x.OwnersId == null);

Another option is to check HasValue property:

List<Car> cars = await carsContext
    .Query(x => x.Id == model.CarId && !x.OwnersId.HasValue);

Though if this will translate into valid SQL depends on the ORM you are using.

CodePudding user response：

The 'Value' property will never be null. If the OwnersId is null then calling .Value would throw an exception. You should check against HasValue. So you can do this:

List<Car> cars = await carsContext.Query(x=>x.Id== model.CarId && !x.OwnersId.HasValue);